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Surface Areas And Volumes

Question
CBSEENMA9003180

Construct the following angles and verify by measuring them by a protractor:

105°

Solution

105°
Given: A ray OA.
Required: To construct an angle of 105° at O.
Steps of Construction:
1. Taking O as centre and some radius, draw an arc of a circle, which intersects OA, say at a point B.

2. Taking B as centre and with the same radius as before, draw an are intersecting the previously drawn arc, say at a point C.
3. Taking C as centre and with the same radius as before, draw an arc intersecting the arc drawn in step 1, say at D.
4. Draw the ray OE passing through C. Then ∠EOA = 60°.
5. Draw the ray OF passing through D. Then ∠FOE = 60°.
6. Next, taking C and D as centres and with the radius more than 1 half CD, draw arcs to intersect each other, say at G.
7. Draw the ray OG intersecting the arc drawn in step 1 at H. This ray OG is the bisector of the angle FOE, 
straight i. straight e. space angle FOG equals angle EOG equals 1 half
angle FOE equals 1 half left parenthesis 60 degree right parenthesis equals 30 degree
Thus comma space angle GOA equals angle GOE plus angle EOA equals 30 degree plus 60 degree equals 90 degree
8. Next, taking H and D as centres and with the radius more than 1 half HD, draw arcs to intersect each other, say at I. 9. Draw the ray OI. This ray OI is the bisector of the angle FOG, 
straight i. straight e. comma space space angle FOI equals angle GOI equals 1 half
angle IOG equals 1 half left parenthesis 30 degree right parenthesis equals 15 degree
Thus, ∠IOA = ∠IOG + ∠GOA = 15° + 90° = 105°. On measuring the ∠IOA by protractor, we find that ∠IOA = 105°.
Thus, the construction is verified.